An Arctic methane worst-case scenario

Let’s suppose that the Arctic started to degas methane 100 times faster than it is today. I just made that number up trying to come up with a blow-the-doors-off surprise, something like the ozone hole. We ran the numbers to get an idea of how the climate impact of an Arctic Methane Nasty Surprise would stack up to that from Business-as-Usual rising CO2

Walter et al (2007) says that Arctic lakes are 10% of natural global emissions, or about 5% of total emissions. I believe that was considered to be remarkably high at the time but let’s take it as a given, and representing the Arctic as a whole. If the number of lakes or their bubbling intensity suddenly increased by a factor of 100, and it persisted this way for 100 years, it would come to about 200 Gton of carbon emission, which is on the same scale as our entire fossil fuel emission so far (300 Gton C), or roughly the amount of traditional reserves of natural gas (although I’m not sure where estimates are since fracking) or petroleum. It would be a whopper of a surprise.

Scaling Walter’s Arctic lake emission rates up by a factor of 100 would increase the overall emission rate, natural and anthropogenic, by about a factor of 5 from where it is today. The weak leverage is because the high latitudes are a small source today relative to tropical wetlands and anthropogenic sources, so they have to grow a lot before they make much difference to the sum of all sources.

The steady-state methane concentration in the air scales nearly linearly with the emission rate. Actually, the concentration goes up somewhat faster than a constant times the emission rate, because the lifetime in the atmosphere gets longer (IPCC TAR). Let’s err on the side of flamboyance (great word in this context) and say the concentration of methane in the air goes up by a factor of 10 for the duration of the extra methane emission (meaning that the lifetime doubles).

Using the modtran model on line I get a radiative forcing from 10 * atmospheric methane of 3.4 Watts/m2 (the difference in the instantaneous IR flux out, labeled Iout, between cases with and without 10x methane). Using the TAR estimates of radiative forcing gives 2.7 Watts/m2.

But methane is a reactive gas and its presence leads to other greenhouse forcings, like the water vapor it decomposes into. Hansen estimates the “efficacy” of methane radiative forcing to be 1.4 (Hansen et al, 2005, Shindell et al, 2009), so that puts us to 4 or even 5 Watts/m2.

This is about twice the radiative forcing today from all anthropogenic greenhouse gases today, or (again according to Modtran) it would translate to an equivalent CO2 at today’s methane concentration of about 750 ppm. That seems significant, for sure.

Or, trying to “correct” for the different lifetimes of the gases using Global Warming Potentials, over a 100-year time horizon (which still way under-represents the lifetime of the CO2), you get that the methane would be equivalent to increasing CO2 to about 500 ppm, lower than 750 because the CO2 forcing lasts longer than the methane, which the GWP calculation tries in its own myopic way to account for.

But the methane worst case does not suddenly spell the extinction of human life on Earth. It does not lead to a runaway greenhouse. The worst-case methane scenario stands comparable to what CO2 can do. What CO2 will do, under business-as-usual, not in a wild blow-the-doors-off unpleasant surprise, but just in the absence of any pleasant surprises (like emission controls). At worst comparable to CO2 except that CO2 lasts essentially forever.

159 Responses to “An Arctic methane worst-case scenario”

Methane alarmism will not be dissuaded by any reasonable means. But nice try David. ;)

[Response:Well, to be honest, sometimes I do get spooked myself. There is a lot of carbon up there. David. PS: On further reflection, I don’t think I want to be fighting being alarmed about methane bubbles in the Arctic. I am alarmed too, but perhaps I’m alarmed for a longer time frame than some. David]

#41 Anonymous Coward (for the first time, we have two ACs in the same thread!),
Methane emissions can have two effects which should not be confused:

1 – they can increase the amount of atmospheric methane (short-term effect)
Methane form rice paddies does this.
Methane from permafrost does this. It is currently ot a large source compared to livestock, rice paddies and so on.

2 – they can increase the amount of carbon in the system (long-term effect)
Methane from rice paddies doesn’t do this. It is carbon neutral.
Methane from permafrost does this. This carbon has been out of the system for a long time. It is currently not a large source compared to the burning of coal and other fossil fuels.

“…The PETM was also a slower release, taking 10,000 years they say from sediment core chronology. David”

David, I havent been keeping up with all the PETM research, but I do recall that individual plankton recovered from Bass River, New Jersey show a single step CIE. Due to the high sedimentation rate of coastal fluvial systems, Bass River sediments are consistent with a much shorter duration of organic carbon release during the PETM (estimated as less than 500 years). From Zachos (2007), http://www.es.ucsc.edu/~jzachos/pubs/Zachos_etal_RoyS_07.pdf.

Does this conclusion hold in the PETM community? Or does the community just ignore the Bass River record entirely because plankton abundance and/or sedimentation could have been temporarily and drastically disrupted at this site in response to the environmental effects of the PETM?

[Response:My recollection is that Zachos had the same observation from ODP cores, that surface-dwelling forams were either isotopically heavy or light, never transitional, but bottom-dwellers could be found with transitional isotopic composition. It does sound to me a lot like an instantaneous atmospheric release, with the benthic forams recording the transition due to slow ocean overturning. But Jim feels that the intense dissolution right at that time could have erased the transitional plankters, caused by the CO2 and evident in a low- or no-CaCO3 layer in the cores. David]

“Most ecosystems were able to adapt—tropical mammals migrated to North America and Europe, and sea life swam poleward to cool down. But the rate of warming during the PETM pales in comparison to what we’re now experiencing. … at a rate that is too fast for ecosystems to adapt …”http://www.wunderground.com/climate/PETM.asp

And yes, we know the rates of change, and of adaptation.
Or at least the scientists do.

“…we must expect sea water to penetrate the permafrost under it and displace all of the free methane currently trapped under the permafrost. The formation of undersea thermokarst results in more rapid release of free methane from formations capped by permafrost than the progressive and uniform melting model.”

This is something that I am also thinking about. In this context i wonder if the simple models described in

can be improved by adding in thermokarst mechanisms. Much more heat can be injected by moving bulk water than in a diffusive process. Thermokarst collapse would also lead to isolated blocks of permafrost with larger surface area to volume ratio, which would be more easily melted.

It’s a bit of a high-wire act. We need to not be alarmist about the potential of this alarm, but realize that it is something to be alarmed about if we let this ‘little’ global warming thing go too far… on top of the other reasonably alarming things that are already going on, such as hitting thermal limits for crops, etc.

Too many uncertainties around what we will or won’t do on mitigation at this time, as well as when and how much methane will release…

So, yes, there is risk, and the risk has alarming components to it. Best to exercise the precautionary principle and not to play with fire too close to the methane bubbles :)

I find it difficult to take this article seriously when its sole aim appears to be showing that rising CH4 emissions are not a problem now and are unlikely to be for a millennia. This task is made easier by not quantifying the likely magnitude of CH4 deposits in the Arctic, not specifying CH4 sources (hydrates, sedimentary gas, yedoma and resumption of biota decay), and not examining the differing vulnerability of those deposits to global warming in general and Arctic amplification in particular. Should one expect a more rigorous approach from a scientist?

Alan Roth @ 30 makes some valid points particularly in relation to the GWP of methane (CH4) which most peer-reviewed papers state as 20-25 over a 100 year time line. This ignores the fact that CH4 is normally resident in the atmosphere for 8-12 years only and during that period has GWP of ~80. It is true that a large emission of CH4 over a short period, say 5 gigatonnes over 12 months, could take 20 years to oxidise to CO2 but even over this period, CH4 has GWP of ~70.

To persist with citing GWP over a century is misleading and results in the warming effects of CH4 emissions being understated. To contend that rapidly rising temperature in the Arctic – both atmospheric and seabed – do not currently pose a serious risk of increased CH4 emissions this century is equally misleading. To not refute but simply to ignore the findings of scientists undertaking field-work over, on and under the continental shelf, even when peer-reviewed and published, seems an odd way of conducting scientific inquiry which purports to reach sound conclusions.

Again, you know better than to get excited over a single measurement. It tells us nothing. It is an interesting event, something to research, and perhaps to give us a better understanding of the carbon cycle in the Arctic. What is more, the numbers themselves are not yet even scary. Ask yourself: how would you respond to a denialist crowing about a single dropoff in CH4 or CO2? What matters are trends. A single observation doesn’t give you a trend.

I was once on a focus group run by Simon Schackley, now of the UK Biochar Research Centre. Over a series of Monday evenings, I became convinced that CO2 storage in underground geological structures was sound if porous rock capped with clay was used. There are some very large suitable structures off the coast of the UK.

I think any techniques to take CO2 from the air are just a matter of the price we put on CO2 extraction. To stop dangerous climate change it may be necessary to have a high tax on carbon. In the UK, if we were to count the £0.80p per litre tax on liquid transport fuel as a tax on carbon dioxide it would be about £300 per tonne.

This tax is clearly insufficient to suppress enough CO2 from transport so perhaps we should aim higher. I suggest two figures £500 and £1000 per tonne of CO2 as reference. (It may also be interesting to contemplate a lower figure, say £200 per tonne, and argue that much of the current tax on transport fuel is to cover externalities such as noise, congestion, ill health and death.)

I think that these prices would enable substantial extraction of CO2 from the atmosphere and I would expect the market to respond to this challenge within a small number of years.

Since you made it personal, let me follow suit: This alarmist has been right for the last five years. Just sayin’.

And, please, can we show a little respect for each other? Alarmist, as used here is no better than denialist. While the latter is well deserved, the latter will only be known in time, and thus far, at least in my case, is completely inaccurate. Or hould I call everyone else underestimatists?

;-)

Thanks for the math note. LOL… One should never edit their own work.

Finally, my little series there is fully justified, but not an assumption, just an example that the worst case is not even approached by David’s piece. The justifications are simple: we have examples, though very short term, of orders of magnitude faster destabilization than mere doublings in the Arctic already. We also have an assessment from Hansens, et al., that Greenland melt may average out to a doubling every decade. Given the nature of Arctic Amplification, why would we expect that to be less in a further north and more complex system? That seems like a rather risky bet.

Ray! I’m a systems guy! I design systems to be massively integrated and based in natural systems using natural patterns. Asking me to look at a destabilizing, massively complex system and assume it’s going to do *less* than expected? Not bloody likely. The fact I’ve been saying for so long the system was going to destabilize much faster than most of you were willing to state is a direct result of me seeing this entire system as one.

That one measurement is not a single measurement for me, it’s a part of a *really obvious* pattern, nested patterns, even.

I find it amazing that the methane alarmists in this thread are saying that methane’s GWP understates the importance of methane.
They may be misleading a good many readers.

Are you aware that CH4 concentrations have increased about 1 ppm in the last 200 years?
Do you understand what forcing that would imply if methane was such a powerful greenhouse gas?
The reason the post-industrial CH4 forcing is not in the same league as the post-industrial CO2 forcing is that GWP exagerates the impact of methane realtive to carbon dioxide by a factor of 2.75.
When CH4 turns into CO2, the forcing caused by that carbon atom is divided by about 25, not >70!

David B. Benson @63. I mentioned @30 that the abrupt change is specific to the Arctic but that there will be global consequences. If the top 3+ meters of the permafrost are to thaw this century under a scenario that was developed before the unexpected extensive melting of sea ice, the 900 billion tons of carbon that were to come from this thawing would likely move into the atmosphere over a shorter span of time. To the extent the carbon emissions are largely methane, at least early on, the threat is enormous, dwarfing CO2 emissions. That is with methane’s GWP of 100 at the time of emission diminishing to 72 20 years later. All projections must be judged by probability and I give it a relatively high probability. But others may say that the devil is in the details and there are many.

For example, how good is the estimate of carbon abundance to 3 meters depth? How good is the CCSM3 model or other models to estimate thaw rate? How much will sulfate-reducing bacteria lower the methane emission rate? How long will soils remain hydrated enough to produce methane over CO2? How long will methane emissions remain in the Arctic to radiate back onto the permafrost? Are there any unseen precursors to OH that would come into play to remove more of the methane? Can the increased thermal energy content of Arctic waters move over the permafrost enough to seriously increase methane emissions? These are all relative unknowns that need further study. But would they significantly reduce the probability that methane emissions from the permafrost will greatly increase global temperature sooner than later?

There are likely to be some factors that will reduce this threat while others will increase it. Then there would be the positive feedback such as warming the Arctic waters enough to destabilize clathrate reserves. One might expect some clathrate release in the Arctic, perhaps not enough to greatly affect global warming by itself, but add this to the increased thermal energy and methane radiation already on the increase in the Arctic and the combination increases risk.

A key component I’ve not seen mentioned enough is the runoff from rivers directly into the Arctic basin. Those waters are heavier than the salty water of the ocean. They should be assumed to flow along the sea floor to some extent… and we don’t need much extent for that for it to begin to warm clathrates, do we?

What makes river water “heavier” than salty sea water? Salt water has higher density than fresh. You may want to review some of the basics at WikiPedia.

When correcting people better informed than yourself you need to check every detail (sorry, Gavin :).

Optimist: “The worst case scenario for methane is the same as our CO2 emissions, but methane emissions haven’t taken off yet and are currently 100x lower than the worst case scenario. Since CO2 is the major current forcing, CO2 is the real worry.”

Pessimist: “The worst case scenario for methane is the same as our CO2 emissions, except that once the emissions really get started it will be impossible to stop them. By the time we notice any increase in methane production, it will already be too late. Since CO2 emissions are in principle controllable while methane emissions are not, methane is the real worry.”

Current Arctic warming is largely driven by massive changes in heat exchange processes, from a once very short summer weather period to much longer ones in less than ones lifetime. It is this process change which I observe, and also the dimming of winter overall strength, once seen by strong refraction events. More frequent incursions of warmer low pressure Cyclones from the South bring heat which destroys surface boundary layers and changes twilight brightness. All of which has a severe influence on permafrost, once reinforced by colder winters having effectively an insulating steady surface air layer , now much weakened, allowing apparently lower spring and fall sun rays to have greater impact. The only limitation factor is the long night, which instantly cools the atmosphere. The limit of outgassing is thus left to how open the Arctic Ocean is, open water essentially represents summer, even in darkness, since the surface of the sea is much warmer than the long night lower atmosphere. If coastal Arctic open water lasts all year, I am sure that all estimates are off. Winter defined by sea ice has to be watched closely. The bubbling now seen may spread wider as summer weather wins the Arctic.

And, since worry by itself accomplishes exactly nothing, aren’t the policy actions mostly the same–ie., mitigating all anthropogenic GHG emissions, beginning with the most amenable and working toward the more obdurate?

The loss of ice cover not only means that more open water will be around to directly warm the air into the Arctic night, but that more water vapor will be around to hold heat in. It is not only how much heat there is, but how long it lasts.

Does anyone know if the models consider that, as the Arctic becomes more and more ice free, we are getting a entire new ocean as a source for the strong GHG water vapor? That would seem to be a pretty powerful feedback in that region, but perhaps I am overlooking something?

This is at the core of what make AGW so dismal. Normal (!) AGW due to CO2 is like imagining turning around an oil tanker by throwing feathers at it. If we don’t change our behavior, in 50 years we’ll be on a planet inhospitable to modern civilization. And then [in a stage whisper] we might be wiping out 80% of what’s left 1000 years from now due to CH4. The stakes are so high. The consequences so far removed. You’d feel goofy believing it if it weren’t for the math and visible edges starting to fray.

If the number of lakes or their bubbling intensity suddenly increased by a factor of much more than 100, and it persisted this way for much more than 100 years.will it suddenly spell the extinction of human life on Earth?

[Response: No. It would certainly be extremely disruptive and I wouldn’t like to imagine how it would all play out, but extinction is really high bar to reach (really, nowhere on Earth could support humans?), and it does very little good to frame things as if that was the issue. – gavin]

I agree with a good deal of what you say. However, it’s important to look at things as objectively as possible.
There may well be 900 GT carbon locked in permafrost.

Thawing of said permafrost doesn’t mean it’s all going to be released to the atmosphere. For example, there are huge peat reserves in Indonesia which is a long way from freezing. Some portion will be released; some as methane. That’s reason enough to keep it frozen as far as I’m concerned.

“In this paper we present new data from ship-based measurements and two-year observations from moorings in the Laptev Sea along with Russian historical data. The observations from the Laptev Sea in 2007 indicate that the bottom water temperatures on the mid-shelf increased by more than 3�C compared to the long-term mean as a consequence of the unusually high summertime surface water temperatures. Such a distinct increase in near-bottom temperatures has not been observed before…Strong polynya activity during March to May 2007 caused more summertime open water and therefore warmer sea surface temperatures in the Laptev Sea. During the ice-free period in August and September 2007, the prevailing cyclonic atmospheric circulation deflected the freshwater plume of the River Lena to the east, which increased the salinity on the mid-shelf north of the Lena Delta. The resulting weaker density stratification allowed more vertical mixing of the water column during storms in late September and early October, leading to the observed warming of the near-bottom layer in the still ice-free Laptev Sea… Warmer water temperatures near the seabed may also impact the stability of the shelf’s submarine permafrost.”

So there are direct measurements that the bottom of the Arctic Ocean is getting significantly warmer. If I understand correctly, most of the top of the methane hydrate level is right at the edge of destabilization. ANY increase in temp should be able to destabilize it. I would think that 3 degrees would be more than enough, especially after a few years of that heat radiating through any sediment that is between the water and the hydrate or permafrost.

The mechanisms for a whole lot of subsea permafrost and hydrate destabilizing surely seem to be in place, and any pools of free methane beneath that would likewise likely rapidly degas.

As Shakhova said back in 2010, sudden release of as much as 50Gt of methane from these sources is possible at any time.

All of this is reason for everyone and his brother, aunt and sister to greatly reduce their own GHG emissions, and to scream bloody murder till every corporation, institution and governmental body they have any influence over to immediately institute policies to rapidly bring down GHG emissions and look at reliable ways of drawing down atmospheric CO2 levels directly (especially replanting grasslands in the north, tree planting toward the equator where albedo change is not an issue).

A 2 degree C increase in global temperature from the mid-20th century average is considered dangerous warming by many of our governments. It’s been estimated by the same that an average atmospheric carbon dioxide concentration of 450ppm would produce such an increase. Any additional, unplanned, positive temperature forcing from methane is unwelcome.

A 2 degree C increase will result in perhaps the extinction of a third of our planet’s species of fish, animals and plants, the future loss of coastal environments dependent on a stable sea level such as the vast marshes along the micro-tidal Gulf of Mexico coastline and many of world’s river deltas, the loss of temperate forest cover as is already occurring, the reduction in seasonal snow and ice cover, the warming of ocean water above that favorable for many marine environments, and the increase in the number of summer days when it is too hot for normal outdoor activity in the earth’s warmer climates.

It’s a matter of opinion of course, shaped by each of our’s particular life style and place of residence; but for me, the world is already heading to global disaster. In regards to this methane kerfuffle, any increase in global temperature forcing is a disaster for me.

For me at least, the environmental changes my children and children’s children will face will be dramatic and for the worse. Many of the things that I love and my children love such as the natural barrier island beaches, the tidal cypress swamps, and the pine forests, all within a half hour drive from our home, will without a doubt be gone by 2100. Human development including the disruption of normal coastal geomorphic forces by coastal infrastructure assure that any change in global temperature and consequent sea level, will be a disaster to these environments. Playing outside is already something few kids do here in the summer (Houston) when the afternoon temperature and humidity combine for a heat index over 105F. Though it doesn’t stop us from venturing out in the morning and evenings. But what about when summer heat indices reach 115F? And don’t cool down below 100F? And what about the poor folks in Houston and the rest of the SE U.S. that don’t have airconditioning? For that matter, what about the folks cutting cane in El Salvador who are already dying at the ripe age of 30 from heat stress?

I’d like to see more discussion of the biological, ecological and lifestyle ramifications of anthropogenic gobal warming discussed at this web site. There have been some excellent summaries of likely future enviroments posted to the GISS web page discussing forest changes changes in afternoon heat indices, etc. This could provide fodder for the team’s posts.

@ 76: “And, since worry by itself accomplishes exactly nothing, aren’t the policy actions mostly the same–ie., mitigating all anthropogenic GHG emissions, beginning with the most amenable and working toward the more obdurate?”

@ 82: “And the answer is the same for all of them, and very well known.”
Is it really?

“mitigate” is a vague general word for many.

In plain English, stop burning carbon. Leave it in the ground.

“… the more obdurate.” like transportation. So Subsidize more rail transport from street cars to high speed long distance rail. Subsidize rooftop solar instead of petroleum. Then make car buyers aware of the lifetime cost of the fuel.

Meanwhile back on the CO2 farm, the 4, 5, or 6C warming we could face in 100 to 200 years, from what I understand, is enough to go on to pretty much destroy most life on earth, though I’m not sure if the time for this to cause tremendous damage and kill off more than half of life is short (a few hundred years) or longer (1000s or 10,000s of years). Does anyone have an idea?

[Response:These are not even remotely answerable in any meaningful way.–Jim]

Another dangerous thing about methane. Apparently in warmer, superanoxic conditions some sea bacteria turn CH4 into H2S (hydrogen sulfide) which kills life, and is thought to have nearly done in what meager life remained during the end-Permian 251 mya after serious 6-8C warming over 10000s of years did a nasty job on life.

So just because CH4 doesn’t all go into the atmosphere or doesn’t seem to be the light-sleeping irracible dragon we made it out to be (which we are compulsively poking with our CO2 emission-caused warming), doesn’t mean it isn’t dangerous.

All near-surface deposits of Siberian CH4, estimated as ~4,000 Gtonnes, are susceptible to warming. Offshore deposits are subject to the effects of ocean warming (3°C in the last 3 decades) all year and a seasonally warming atmosphere. On-shore deposits are affected by atmospheric warming amplified to 2 or 3 times average global warming. It is reasonable to conclude that off-shore deposits are more vulnerable to destabilisation in the short term (within the next 30-50 years) than those on-shore. However modeling by Lawrence at al (2005) shows that by 2100 the top 3 metres of permafrost will be lost and this will have significant effects on CH4 emissions over the next century.

Shakhova points out and Archer clearly recognises that only a small fraction of these vulnerable deposits, around 1% or 2%, have to vent to the atmosphere this century to cause abrupt, irreversible climate change. Knowing that total anthropogenic GHG emissions are unlikely to be curbed for at least a decade; knowing that Arctic amplification is continuing (some argue accelerating) and causing increased destabilization of Siberian CH4 deposits; can we assert, as the article appear to, that this poses no threat? Schuur and Abbott (2011) make just such a claim. Shakhova and Sermiletov (2010) warn that venting of 50 Gtonnes CH4 could occur at any time.

Who are we to believe? Those who are engaged in cutting edge field-work or those who hold more sanguine, possibly less informed views?

David Miller @81. I think you are right that some carbon in the permafrost will remain. I appreciate your comment. I’ll provide some more information about the permafrost process.

I mentioned that the 90% estimate is based on the top 3.34 meters of the permafrost while there is still much below that. A process called cryoturbation occurs with repeated thawing and freezing causing movement of the carbon deep into the soil. Permafrost carbon can be found many hundreds of meters below the surface. While some areas may not lose their carbon to a depth of even 3 meters this century, other areas may lose their carbon at much greater depths well before the end of the century.

I had thought that permafrost starts thawing at the surface and then the warmer temperatures slowly work their way down with lower levels not experiencing a rise in temperature until late in the process. The IPCC FAR WG I Report provides considerable information about temperature rises at low depths. In the Canadian High Arctic, there was warming of permafrost at depths of 15 to 30 meters since the mid-1990s. The increase was about 1 degree Celsius at depths of between 1.6 and 3.2 meters from the 1960s to the 1990s in East Siberia. and from 0.3oC to 0.7oC at a 10-meter depth in northern West Siberia. In northern European Russia from 1973 through 1992 there was an increase of 1.2oC to 2.8oC at a depth of 6 meters. It was also reported that in Central Mongolia at depths from 10 to 90 meters, there was a temperature increase of 0.05oC to 0.15oC per decade over 30 years. In Svalbad, Norway, the permafrost at 20 meters depth has warmed at a decadal rate of about 0.5oC. [citations for all of the above can be found at http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter4.pdf page 371]

At a June 2006 Symposium, Dr. Katey Walter said, “The rapid thaw of permafrost can release this carbon nearly instantaneously, raising atmospheric carbon concentrations.” She went on to say that significant permafrost thaw is likely by 2100 and perhaps most of it will thaw by then.

Studies of current permafrost have led to conclusions about what might have happened as the last glacial period ended and the glaciers receded from a 3-million square kilometer area in Europe and south of West Siberia. The soils may have similarly held organic matter and experienced a carbon loss from the permafrost which would have contributed to past changes in atmospheric CO2 concentrations. Permafrost soil which is rich in carbon holds on average about 2.6% carbon per square meter. In this post-glacial region, the carbon depth was estimated to be about 4 meters. This would yield an average of about 30 kg of carbon per square meter. It is therefore estimated that about 500 billion tons of carbon were emitted into the atmosphere at the end of the last glacial period. The current soils in that region now have about 0.15% carbon compared to the earlier 2.6%. (Zimov, Permafrost and the Global Carbon Budget) There was no mention of how much time this would have taken.

I think that we have still a lot to learn before we can speak with more certainty. But it’s a game of probability and the situation in the continuous permafrost area raises great concern.

Our emissions policies should be driven by the worst case, since the worst case is truly catastrophic to life on earth. Your elaboration of our future confused me- if worst case methane bursts are roughly equivalent to CO2 emissions.

1) The idea that melting stuff can increase GH emissions. That must have happened before. Imagine a huge methane reserve pimple spurting into the atmosphere like a super volcano.
2) The abstract fun associated with this idea. Honestly, it reminds me of the partisan ideas of W. E. over at wupwiththat.com. Why should it be fun? It’s horrifying.

It’s quite a relief to know that massive releases of methane won’t “abruptly” kill off humanity. That the disruptions of just about every aspect of climate and weather could drag on for a long period would would make the experience much more … interesting.

Not a word in the piece about surprises – the unexpected things nobody thought about, or properly factored into the bigger picture. In times past I was impressed by the “mousetrap” scenarios. Push something to the breaking point – like the catch on the rodent trap – and something gives way.

Lately my earthquake insurance has taken a big jump. Considering how I’m on the most distant fringes of the New Madrid fault, I wondered what Big Insurance knew that I didn’t. Well, it turns out if you ‘lubricate’ an underground fault it’ll be more likely to break loose. Fracking anybody? And who expected the most inert of chemicals (according to my sixties-era high school science books) – the CFCs – would eat the ozone layer?

But we can relax. Only the Business As Usual scenario with regulation CO2 is worrisome. Methane is NOT something which ought to cause us any concern. Just relax about that one.

Except for the numbers of intelligent remarks in the comments here, I’d be taking down the link to this site about now.

Well, admittedly, the PETM was a natural rate of change.
Any methane spike from human warming _will_ happen a lot faster as the warming’s a lot faster, won’t it?

What else is different? Well, there’s — fertilizer, vast amounts of nitrogen at an equally high rate of change. Like sulfate and CO2, nitrogen and methane may mask one another’s effects at least for a while or until one gets limited.

We got a bit surprised finding that removing sulfates removed a negative forcing on warming.

What happens if we clean up our nitrogen pollution problem — due both to agricultural overuse getting into the air, and to internal combustion engines burning nitrogen. Do we then see a lot more methane accumulating?

More work on explaining methane genesis, also explains better the PETM event.

Inland waters take in organic carbon and emit methane

Extreme organic carbon burial fuels intense methane bubbling in a temperate reservoir – Sobek et al. (2012)
Abstract: “Organic carbon (OC) burial and greenhouse gas emission of inland waters plays an increasingly evident role in the carbon balance of the continents, and particularly young reservoirs in the tropics emit methane (CH4) at high rates. Here we show that an old, temperate reservoir acts simultaneously as a strong OC sink and CH4 source, because the high sedimentation rate supplies reactive organic matter to deep, anoxic sediment strata, fuelling methanogenesis and gas bubble emission (ebullition) of CH4 from the sediment. Damming of the river has resulted in the build-up of highly methanogenic sediments under a shallow water column, facilitating the transformation of fixed CO2 to atmospheric CH4. Similar high OC burial and CH4 ebullition is expected in other reservoirs and natural river deltas.”

The sudden release of large amounts of natural gas from methane clathrate deposits in runaway climate change could be a cause of past, future, and present climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; it is thought that this is a main factor in the global warming of 6°C that happened during the end-Permian extinction as methane is much more powerful as a greenhouse gas than carbon dioxide (despite its atmospheric lifetime of around 12 years, it has a global warming potential of 72 over 20 years and 25 over 100 years). The theory also predicts this will greatly affect available oxygen content of the atmosphere. Source Clathrate Gun Hypothesis http://en.wikipedia.org/wiki/Clathrate_gun

Focusing on the Permian-Triassic boundary, Gregory Ryskin [1] explores the possibility that mass extinction can be caused by an extremely fast, explosive release of dissolved methane (and other dissolved gases such as carbon dioxide and hydrogen sulfide) that accumulated in the oceanic water masses prone to stagnation and anoxia (e.g., in silled basins). http://en.wikipedia.org/wiki/Clathrate_gun

I’ve been reading Real Climate since it’s inception and find the current thread to be the most interesting yet. As a layman, I often struggle and sometimes fail to keep up. Thanks for exploring these issues in this public forum.

ah Proc, forget the “fast, explosive” pimple-popping notion.
Seriously, if you want to rely on Wikipedia, read the first page you cited:

“… “clathrate gun” … abrupt runaway warming in a timescale less than a human lifetime …. is now thought unlikely.[3][4]
… there is stronger evidence …., over timescales of tens of thousands of years ….”

At this level of emissions, the chance of radiatively important mesospheric clouds forming would increase. Hansen et al. considered increased stratospheric water vapor as an indirect forcing from methane, but they do not consider the broadband infrared properties of ice crystals in the Efficacy paper. There is also feedback to stratospheric ozone abundance owing to solid phase chemistry on the crystal surface. There may be more to consider under such a high emissions scenario.